We have employed hard x-ray photoemission (HAXPES) to study a delta-doped SrTiO 3 layer that consisted of a 3-nm thickness of La-doped SrTiO 3 with 6 La embedded in a SrTiO 3 film. Results are compared to a thick, uniformily doped La:SrTiO 3 layer. We find no indication of a band offset for the delta-doped layer, but evidence of the presence of Ti 3 in both the thick sample and the delta-layer, and indications of a density of states increase near the Fermi energy in the delta-doped layer. These results further demonstrate that HAXPES is a powerful tool for the non-destructive investigation of deeply buried doped layers.
Bibliographical noteFunding Information:
Travel and salary support for A.X.G. and A.K. was provided by the MURI program of the Army Research Office (Grant No. W911-NF-09-1-0398). Two of us (C.S.F. and G.C) also acknowledge salary support from the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Research at Stanford was supported through the Stanford Institute for Materials and Energy Science (SIMES) and the LCLS by the US Department of Energy, Office of Basic Energy Sciences. The HAXPES measuements at BL15XU of SPring-8 were performed under the approval of NIMS Beamline Station (Proposal No. 2010B4800). The authors are grateful to HiSOR, Hiroshima University and JAEA/SPring-8 for the development of the HAXPES station at BL15XU of SPring-8. S.S. also acknowledges funding from NSF (Grant No. DMR-1006640). The HAXPES instrument at beamline P09 is jointly operated by the University of Würzburg (R. Claessen), the University of Mainz (C. Felser) and DESY. Funding by the Federal Ministry of Education and Research (BMBF) under contracts 05KS7UM1, 05K10UMA, 05KS7WW3, and 05K10WW1 is gratefully acknowledged.